1. Field of the Invention
The present invention relates to a coating apparatus and a coating method.
2. Background Art
Coating apparatus of the single wafer processing type is commonly used to manufacture an epitaxial wafer, which is a wafer with a single crystalline film of silicon, etc. grown thereon.
A common coating apparatus of the single wafer processing type includes a chamber, gas supply means, wafer heating means, etc. The chamber contains a susceptor for supporting a wafer, and this susceptor can be rotated by a motor. In such a coating apparatus, the wafer placed on the susceptor is heated by wafer heating means while being rotated, with the wafer heating means being disposed above and below the susceptor. At that time, a reactive gas is supplied through the gas supply means to form an epitaxial film uniformly on the wafer.
In order that the epitaxial film formed on the wafer may be uniform in electrical characteristics, etc. across the entire surface of the wafer, it is necessary to equalize the flow of gas in the chamber. To achieve this, a distributor plate (or shower head) of quartz is provided at the top of the chamber so that the reactive gas supplied from the gas supply means is uniformly applied over the surface of the wafer.
Incidentally, it has been found that the formation of a thick epitaxial film on the wafer is accompanied by the formation of a film on the surface of the distributor plate, since the increased processing time results in an increase in the temperature of the distributor plate due to the radiant heat. If this film peels or flakes off, the flakes cause a reduction in the manufacturing yield of the epitaxial wafer. Furthermore, this film formed on the surface of the distributor plate interferes with the measurement of the wafer temperature by a radiation thermometer disposed at the top of the chamber.
Japanese Laid-Open Patent Publication No. 2008-1923 discloses a coating apparatus which includes a cooling unit for cooling the distribution plate (or shower head). The cooling unit includes a disc-shaped base and a large number of fins extending upward from the top surface of the base. A cooling gas is flowed along these cooling fins on the surface of the base to cool them.
Thus, in the coating apparatus disclosed in this publication, a cooling unit is provided on a member serving as a distributor plate and is cooled thereby cooling the adjacent distributor plate. That is, the distributor plate is indirectly cooled only from one side, meaning that it takes considerable time to cool the entire distributor plate. Therefore, this cooling construction may not be able to sufficiently cool the distributor plate if there is a significant rise in the temperature of the distributor plate, resulting in inability to prevent the formation of a film on the plate.
Further, for example, the distributor plate may be closely spaced from the wafer to increase the reaction efficiency over the surface of the wafer when a film is formed thereon. In such a case, the side of the distributor plate that faces the wafer is heated to a higher temperature than the other opposing side. In the construction of the above publication, however, since the cooling unit is disposed on the side of the distributor plate opposite that facing the wafer, the unit may not be able to sufficiently reduce the temperature rise of the distributor plate. The same problem arises when the wafer heating means is provided at the top of the chamber and the cooling unit is disposed on the side of the distributor plate that faces the wafer. Specifically, in this case, since the distributor plate is disposed between the wafer heating means and the wafer, the side of the distributor plate opposite that facing the wafer is heated to a higher temperature. This means that also in this construction the cooling unit may not be able to sufficiently reduce the temperature rise of the distributor plate.
In the coating apparatus disclosed in the above publication, the cooling unit is made of aluminum. Therefore, in order to measure the temperature of the wafer using the radiation thermometer disposed at the top of the chamber, the cooling unit must be disposed so as not to interfere with this measurement by the thermometer.
Further, this coating apparatus is also disadvantageous in that the cooling unit has a complicated structure since the cooling gas flows along the cooling fins on the surface of the base.
The present invention has been made in view of these problems. It is, therefore, an object of the present invention to provide a coating apparatus constructed such that the measurement of the wafer temperature is facilitated and the temperature rise of the distributor plate is sufficiently reduced.
Another object of the present invention is to provide a coating apparatus which has a simple structure, yet in which the temperature rise of the distributor plate is reduced.
Still another object of the present invention is to provide a coating method capable of forming a film while sufficiently reducing the temperature rise of the distributor plate.